Optical fibers are fundamental components in modern telecommunications systems and sensing systems. A typical optical fiber includes a core of a first index of refraction surrounded by a cladding of a second lower index of refraction. Optical fibers are typically made of high-purity silica with minor concentrations of dopants to control the index of refraction. Light rays impinging upon the core at an angle less than a critical acceptance angle undergo total internal reflection within the fiber core and pass through the fiber with minimum attenuation. This enables optical fibers to transmit optical signals containing a large amount of information over long distances with very low loss.
Designs for optical fibers vary depending upon the application, the desired mode of transmission of the light beam, and the materials used in fabrication. Some optical fiber designs use tapered fiber structures (e.g., fibers having a gradually decreasing outer diameter) for coupling fibers together and for making small fiber tips for probes or sensors. For example, tapered fibers for use in coupling are disclosed in U.S. Pat. No. 5,729,643, issued Mar. 17, 1998 to Hmelar, et al., "Tapered Composite Optical Fiber and Method of Making the Same"; U.S. Pat. No. 4,931,120, "Method of Tapering End of Capillary Tube Bore for Optic Fiber Coupling, and U.S. Pat. No. 4,671,609, "Coupling Monomode Fiber Having a Tapered End Portion." Tapered fibers used as probes or sensors are disclosed in U.S. Pat. No. 5,430,813, issued Jul. 4, 1995 to Anderson et al., "Mode-matched, Combination Taper Fiber Optic Probe,"; U.S. Pat. No. 5,703,979, "Cylindrical Fiber Probe Devices," assigned to Lucent Technologies, Inc., the assignee herein; and U.S. Pat. No., 5,093,569, "Tapered Optical Fiber Sensor."
Advancements in optical fiber systems, such as telecommunications systems, have created a need for other types of optical fiber designs, such as optical fiber-based modulators and attenuators. Unfortunately, existing designs are expensive and difficult to implement. Accordingly, there is a need for improved optical fiber-based modulators and attenuators and optical fiber systems which use them.